biostudies-literatureUnknown43(2)Soler JJSibling cannibalism is relatively common in nature, but its evolution in birds and certain other vertebrates with extended parental care had been discarded. Here, however, we demonstrate its regular occurrence in two European populations of the Eurasian hoopoe (<i>Upupa epops</i>) and explore possible adaptive and non-adaptive explanations. Results showed that sibling cannibalism was more frequently detected in Spain (51.7%) than in Austria (5.9%). In these two populations, the hoopoes laid similar clutch sizes, resulting in similar fledging production, but hatching failures were more frequent in the northern population. Consequently, having more nestlings condemned to die in the southern population may explain the higher incidence of sibling cannibalism. In accordance with this interpretaZoological research265-274https://www.ebi.ac.uk/biostudies/studies/S-EPMC8920838biostudies-literatureAvian sibling cannibalism: Hoopoe mothers regularly use their last hatched nestlings to feed older siblings.PMC8920838Martinez-Renau EHoi HMartin-Vivaldi MEckenfellner MSvetlik JMazorra-Alonso MSoler JJRuiz-Castellano CNuhlickova SfalseAvian sibling cannibalism: Hoopoe mothers regularly use their last hatched nestlings to feed older siblings.Sibling cannibalism is relatively common in nature, but its evolution in birds and certain other vertebrates with extended parental care had been discarded. Here, however, we demonstrate its regular occurrence in two European populations of the Eurasian hoopoe (<i>Upupa epops</i>) and explore possible adaptive and non-adaptive explanations. Results showed that sibling cannibalism was more frequently detected in Spain (51.7%) than in Austria (5.9%). In these two populations, the hoopoes laid similar clutch sizes, resulting in similar fledging production, but hatching failures were more frequent in the northern population. Consequently, having more nestlings condemned to die in the southern population may explain the higher incidence of sibling cannibalism. In accordance with this interpreta2022-01-01T00:00:00Z2022 Mar2025-04-05T11:07:17.609Z2025-04-05T11:07:17.609ZS-EPMC89208383523818410.24272/j.issn.2095-8137.2021.434